1. Technical Field
The present invention generally relates to an image capturing device and an auto-focusing method thereof and, more particularly, to an image capturing device of a camera with a plurality of different fields of view and an auto-focusing method thereof.
2. Description of Related Art
With the development of focusing technologies, camera focusing has evolved from manual-focusing to auto-focusing. Generally, auto-focusing of a conventional digital camera includes contrast detection focusing and phase detection focusing. For contrast detection focusing, a highest contrast value is selected from a plurality of contrast values of images taken by a camera at different focal distances so as to achieve auto-focusing by determining the focal distance corresponding to the highest contrast value as an optimal focal distance of the camera.
On the other hand, for phase detection focusing, a light beam is split by a phase focusing detector into two light beams to be projected respectively onto two optical sensor units of the phase focusing detector to obtain a set of optical sensing signals to achieve auto-focusing by deciding the focal distance and the focusing direction according to phase difference information based on the optical sensing signals.
Since contrast detection focusing relies on contrast variations of images taken by a camera at different focal distances to determine the optimal focal distance, the camera has to compare the contrast values of the images during focusing so as to determine the optimal focal distance for the camera. Accordingly, compared to the camera using phase detection focusing, it takes longer time for the camera using contrast detection focusing to complete focusing.
It should be noted that the camera using phase detection focusing may cause distortion of images when there are provided too many phase focusing detectors in the camera because the optical sensor units of the phase focusing detectors are not suitable for use in generating pixels of images.